Conventionally, in a guideline for making an image diagnosis of emphysema, a cross-sectional image at an axial plane that goes through the top end of the diaphragm is specified as one of medical images that should be referred to by a medical doctor.
For an image diagnosis of emphysema, first, a three-dimensional medical image of a chest of a subject is taken by using a medical image diagnosis apparatus such as an X-ray Computed Tomography (CT) apparatus, an X-ray diagnosis apparatus, a Magnetic Resonance Imaging (MRI) apparatus, or the like. Further, the medical doctor determines the position of the top end of the diaphragm by visually checking cross-sectional images of the three-dimensional medical image at a coronal plane and at an axial plane. After that, the medical doctor makes an image diagnosis by referring to an axial cross-sectional image at the top end position of the diaphragm and a coronal cross-sectional image in which the top end position of the diaphragm is displayed. More specifically, the medical doctor makes an image diagnosis of emphysema by referring to the size of an emphysema region identified in the cross-sectional images.
It is also known that emphysema makes the position of the diaphragm lower and that interstitial pneumonia makes the position of the diaphragm higher. For this reason also, the position of the top end of the diaphragm is important when making image diagnoses of respiratory system diseases. The position of the diaphragm is also used for judging movements of an image-taking target site caused by breathing or the like during an MRI image taking process.
To visually determine the position of the top end of the diaphragm, however, the viewer needs to observe a plurality of cross-sectional images. Thus, a lot of labor is required, and the efficiency of the process of making an image diagnosis is therefore low. In addition, in some situations, the top end position of the diaphragm that is visually determined does not have reproducibility. In other words, the top end position of the diaphragm that is visually determined is based on a subjective judgment of the viewer. For this reason, the top end position of the diaphragm may vary among different viewers. In addition, the top end position of the diaphragm may vary among determining processes that are performed by a single viewer.